Typically, an odor is recognized as a result of intricately combined information associated with different kinds of odor molecules. Therefore, it is extremely difficult to identify an odor by measuring the amount of a single kind of odor molecule. Higher animals recognize an odor through the following mechanism. First, olfactory receptors (approximately ten million olfactory cells), which are present on the olfactory epithelium in the depth of the nasal cavity, recognize individual odor molecules. Then, detection signals of the odor molecules from the olfactory receptors are input, in the form of electrical pulses, to the olfactory bulb located in front of the cerebrum via electrical wires called axons. Finally, the detection signals are transformed into a two-dimensional image represented by an ignition pattern of glomeruli present on the surface of the olfactory bulb.
One type of conventional odor sensing system is configured to have a plurality of odor sensors to identify odor molecules by simulating the above explained odor recognition mechanism of higher animals. In such a conventional odor sensing system, the detection accuracy strongly depends on the number of odor sensors. However, a large number of such odor sensors limits downsizing of the odor sensing system. Due to this, a small odor sensing system capable of detecting a variety of odors with sufficiently high accuracy has not been developed as of yet. Considering the steady expansion in the need for on-the-spot odor sensing, the development of a small, high accuracy odor sensing system is desired.